Workshop consumer unit

[bob_c]

This topic is kind of linked to the 3 phase topic i started about my bandsaw.
Im upgrading the elctrics to my workshop ,i bought this wylex 5 way consumer unit and i need a 32 amp ring off this,a 6 amp light ring and a 16 amp supply which im using just for the bandsaw.
The consumer unit has a 63 amp switch but ive bought seperately a 63 A RCD.(should i just change the switch for the RCD?)
This supply for the workshop consumer unit will be fed from a spare mcb on the house consumer unit(an unused cooker circuit which ive upgraded to 40 amp).
Questions are ,will this be enough to supply the workshop consumer unit?
There wont be much load on it all the workshop machines apart from the bandsaw just plug into the 13 amp sockets.
Also how do i arrange the mcb,rcd,in the workshop unit.Id prefer the light circuit to NOT be fed via the RCD.
One other question i bought by mistake two core swa 6mm cable to feed from the house instead of 3 core.Can i use the armour as the earth or do i need to put a seperate 6 mm earth cable through with the swa .Its going through conduit as well for added protection.
Thanks
A pic of the consumer unit for the workshop.(maybe i should have bought a split unit?)

 

[OLD]

If you do this work as a noncompetent person your doing it at your own risk as this work is notifiable in part p of the regs.
The +ve buss bar is cut after the 6 amp fuse and wired to rcd +ve. -ve is wired to - of rcd and -rcd o/p wired to a new neutral two way made from a suitably rated chockblock.The +ve o/p of rcd is linked to the 32& 16 fuse by the common bar .A proper split load box has all the wires and buss bars as standard.The swa can be used as earth with proper glands fitted and correctly bonded.

 

[StevieB]

Hi Bob, I would seriously suggest getting a proper spark to do this one as from the questions you are asking I do not think you are certain enough as to what you are up to (no offence).

If you have a 40 amp MCB in the house box, what is the point of putting a 63 amp MCB on the other end in the workshop box? The house end will simply trip first.

Personally I would not swap the 63 amp main switch that came with the box for a 63 amp RCD. buy what you need, rather than adapting.

The order of circuits in a box should be highest load next to the breaker. Thus switch, then 32, then 16 then 6. However you could swap the 16 and 32 if there is a big draw on the 16 from your bandsaw and all you usually have is a radio on the 32 ring.

Regarding split load boxes, the only advantage of these is so that if something trips the main fuse in the workshop box (the RCD side) the non RCD side continues to work. Theefore people wire lights to the non RCD side so that if a machine trips the power they are not standing in the dark next to a winding down table saw. For this reason alone I would always put in a split load box. The box you have cannot readily be converted to split load and I would not even try!

Yes, you can use the sheathing in armoured cable as an earth conductor, but make sure it is properly jointed into a metal box with a gland at each end, do not be tempted to bodge an earth wire from the armour to the CU in the workshop.

In short, I would ditch what you have there, buy a small split load box and work from that.

Steve.

 

[Shultzy]

Bob, I've just had the electrics in my workshop wired by my sparky. The armoured cable is fed from the house consumer unit via a 32a mcb to a dust-proof cu in the workshop. All the mcb's are after the 63a rcd as I have installed an emergency light that will come on if the lights fail.

I can take some photo's if you want.

 

[Woody Alan]

Steve

Yes, you can use the sheathing in armoured cable as an earth conductor, but make sure it is properly jointed into a metal box with a gland at each end, do not be tempted to bodge an earth wire from the armour to the CU in the workshop.

Steve are you sure on this, I can't find my copy of the regs at the mo' but I think it may of changed for one of the cores being the required earth, but don't quote me .

As you say that board cannot/should not be converted.

Also to be honest I also have to say if you are asking these questions then you still have a way to go before you understand the full implications of what you are trying to do. As a for instance, Do you know whether your supply is the type that will allow bringing the earth from the main board or maybe it will require an earth spike. If it does how are you going to check the earth impedance. I am not trying to stop you but there are issues around this.

Steve

If you have a 40 amp MCB in the house box, what is the point of putting a 63 amp MCB on the other end in the workshop box? The house end will simply trip first.

Steve this may well be a misunderstanding of the terminology but if he is off a 40A MCB which is fed by a double pole mainswitch and not a ELCB then there is no problem the ELCB 63A is it's max current carrying capacity and is not related to it's ability to trip in a given fault condition. If the 40A MCB is off a ELCB in the house then it may be touch and go as to which one goes out first so really the armoured cable ought to be off an isolator fed off the non trip side of the fuseboard, the cable being protected by the earthed armour which in the event of damage ..spade etc.. would take out the fuse, really no need for an ELCB on this. If you must have it on ELCb then you'll have to invest in a higher speed trip for the workshop. Which when all said and done is why I got my sparky mate to come and give my install the once over and test before connexion and compliance issued.

Alan

 

[Woody Alan]

To follow up my ramblings

- Earthing must be given special attention. All buildings must be provided with 30 mA RCD protection, but the Electricity Supply Company should be consulted to ascertain their special requirements if the supply system uses the PME (TN-C-S) system. Where the supplier does not provide an earth terminal, each outbuilding must be provided with an adjacent earth electrode.

Extract from the regs above. I can't find the ref to needing an earth core conductor if that is the preferred method, but the earth needs to be high quality regardless. The armour needs to be earthed whether or not it "is" earth. Pity Davy Owen isn't around he would make this clear, I am just having a stab at it.

Alan

 

[StevieB]

Not sure of the requirement for the 17th ed of the regs, which come into force in June I believe, but when I did mine a couple of years ago the regs didn't specifically require an earth core. Using the sheathing was allowed.

Any questions like this on electrics can always be asked on the screwfix forum. Its a little more 'robust' than this one in terms of the posters but you will get some good advice if you stick it out. Searching past topics there is also a good way to get an idea as these topics come up again and again.

Steve.

 

[RogerS]

Woody_Alan is correct. You should use one of the cores for the 'proper' earth. You also earth the armoured sheath.